1. Field of the Invention
The invention relates to a fuel filter, in particular a diesel filter, having at least one fuel inlet, at least one fuel outlet, water separator means, at least one sump, a water outlet associated with the sump, and control means for the water outlet.
2. Description of the Prior Art
Fuel filters of the type with which this invention is concerned are used, among other places, in diesel engines for filtering out contaminants contained in diesel fuel and for separating water from the diesel fuel, in order to avoid problems and damage caused thereby, such as contamination or corrosion in the fuel system or poorer combustion in the engine.
One problem of the known fuel filters is carrying the water out of the sump, since after being separated out of the fuel, the water as a rule contains contaminants and therefore must not be given off to the environment without further treatment.
U.S. Pat. No. 4,264,442 discloses a fuel filter having a chamber in which there is a cage defining a fuel inlet chamber which communicates with the fuel inlet, and a fuel outlet chamber located diametrically opposite the fuel inlet chamber and separated from it by a partition, and which communicates with the fuel outlet. The fuel entering the fuel filter via the fuel inlet passes through the fuel inlet chamber, emerges from it via a porous wall into the chamber, circles the cage, then on the opposite side of the cage, via an equally porous wall, it enters the fuel outlet chamber, and from there, via the fuel outlet, it flows out of the fuel filter, as cleaned fuel. The bottom of the chamber outside the cage acts as a sump for water that has been separated out in the filtration. On the bottom of the sump there is a valve, which is controlled with the aid of a water level sensor located in the sump and with which a water outlet, communicating with a line, can be selectively opened and closed. If via the sensor it is ascertained that a certain quantity of water has accumulated in the sump, then the valve is opened, via a negative pressure generated at the water outlet, and a substantial portion of the water is exhausted from the sump by suction and carried away to a downstream chamber via the line.
A substantial disadvantage in carrying water out into such a chamber outside the fuel filter is that the chamber for catching the water must be emptied manually, and in this respect the fuel filter is not maintenance-free.
This disadvantage does not apply to a fuel filter system known from U.S. Pat. No. 4,637,351, which is refined compared to the system known from U.S. Pat. No. 4,264,442 in that the water outlet communicates, via various lines and chambers, with the air intake and exhaust system of the engine and in that way is subjected to a negative pressure. If the water level sensor ascertains a certainty quantity of water in the sump of the fuel filter, then the valve is opened via an electromagnet, so that the water accumulated in the sump is exhausted by suction because of the negative pressure and is delivered to the air intake and exhaust system. The result is that the water drained away evaporates, either upon combustion or at the tailpipe.
Although in this system the water is disposed of directly via the engine, there is nevertheless the disadvantage that connecting the fuel filter water outlet to the engine is complicated and hence expensive. Moreover, on delivering the water into the air intake system of the engine, there is the disadvantage that the combustion air, during the dewatering of the fuel filter, is substantially more humid, which impairs combustion, at least briefly.